Following an intraperitoneal injection of acetaminophen into polycyclic hydrocarbon-responsive mice in which hepatic aryl hydrocarbon hydroxylase (Ah) activity had been induced by pretreatment with polycyclic hydrocarbons, lenticular opacification developed in a few hours. Both Ah ion/Ah ion homozygous and Ah ion/Ah heterozygous inbred mouse strains developed the lenticular opacity. The ciliary body of the eye of polycyclic hydrocarbon-responsive mice was found to posses high activities of Ah and gamma-glutamyl transpeptidase (an enzyme involved in mercapturic acid formation). Therefore, the ciliary body might detoxify hydrocarbons and drugs in the blood at the time of aqueous humor secretion.